Usually, so-called grass cutting heads are used to cut vegetation, for example grass, hedges or the like; these heads are applied to the drive shaft of a bush cutter actuated by an electric motor, an internal combustion engine or other actuating member, for example a hydraulic or mechanical arm actuated by means of a farm machine such as a tractor or the like. The fast rotation of the grass cutting head drives into rotation cutting members, with which the head is provided and which act on the vegetation, cutting it.
In some prior art heads, cut is performed by means of a so-called cutting line, usually made of plastic, for example polyamide (nylon), and housed in a housing of the cutting head that forms an inner space to stock the cutting line. One or more ends of the line project from the grass cutting head; when the head rotates at high speed around its rotation axis, driven by the bush cutter drive shaft, the ends are tensioned due to the effect of the centrifugal force. Thus, the cutting line, tensioned by the centrifugal force, acts on the vegetation and cuts it.
In some applications, the bush cutter is provided with a cutting blade to cut, for example, hedges, small shrubs or the like.
According to the size and resistance of the vegetation, it is necessary to have available different cutting tools or heads, which can be interchanged on the same bush cutter.
Some grass cutting heads are configured to use alternatively a cutting line or one or more cutting blades. EP-A-1364571 discloses a head of this type, wherein the cutting line is disabled when the cutting blades, pivotally mounted on the grass cutting head, are used. When the blades are disabled, the cutting line can be used. These heads do not allow the two cutting members (line and blades) to be used at the same time.
Some grass cutting heads are configured so as to use simultaneously one or more cutting lines and one or more cutting blades in combination. Some grass cutting heads comprise, in combination, cutting members, such as polyamide lines, and cutting blades, usually pivotally mounted on the grass cutting head. These combined heads often use short segments of cutting line, which are anchored at an end thereof to the grass cutting head and shall be replaced when broken. In some cases, the head is formed by the same blade, provided with anchoring points for the cutting lines. Examples of grass cutting heads of this type are described in US-A-2012/0246945; U.S. Pat. No. 4,513,563; EP-A-1997364; U.S. Pat. No. 6,298,642.
GB-A-2000672 discloses a grass cutting head formed by an overturned cup-shaped body that can be coupled to the drive shaft of a bush cutter and covers a cutting line winding spool. Short rectangular blades are pivotally mounted at the sides of the cup-shaped body; when the grass cutting head is driven into rotation, the blades move in radial direction due to the centrifugal force, and cut the vegetation similarly to the line projecting from the spool. This head is poorly efficient and very unsafe for the user.
US-A-2010/0132200 discloses a grass cutting head comprised of a plate forming a cutting line winding spool. Radial cutting blades are mounted on the plate. Also this grass cutting head is poorly efficient, uncomfortable and unsafe for the user.
FR-A-2712136 discloses a grass cutting head with a housing wherein the cutting line is arranged, projecting from the housing by a certain length. The inside of the housing is not shown, and no line-supplying system, i.e. line winding or unwinding system, is described. Below the housing, at a certain axial distance therefrom, a blade with cutting edges is fastened, to which pivoting auxiliary blades are fixed. The structure of the grass cutting head disclosed in FR-A-2712136 is such that the cutting line is necessarily arranged at a large distance from the ground, due to the blade mounting mechanism, below the cutting line housing, which mechanism increases the axial dimension of the grass cutting head. Moreover, as members are not provided to control the cutting line elongation, in order to replace the cutting line length projecting from the housing the user shall handle the grass cutting head in the area where the cutting blades are arranged, and this makes the use of this grass cutting head unsafe and dangerous.
There is therefore a need for a grass cutting head that completely or at least partially overcomes one or more of the drawbacks of the prior art heads.